Evaluation of Multi-Cluster Fracturing Effects in Horizontal Shale Gas Wells Based on Optic Fiber Monitoring Outside Casing

In order to analyze the factors affecting multi-cluster fluid injection during multi-stage fracturing of shale gas horizontal wells, real-time monitoring of the fracturing process was carried out using distributed optic fibers outside the casing. A joint analysis of typical fracturing events and distributed optic fiber acoustic sensing (DAS) signals during multi-stage multi-cluster fracturing process was carried out based on the real-time monitoring data of optic fiber during fracturing of horizontal shale well in the Longmaxi Formation of Zhaotong Shale Gas Demonstration Zone, combined with fracturing design and operation data. The analysis finds that at the initial stage of fracturing, the perforation is not perfect, and near well distortion is serious and easy to trigger strong DAS signals. With the perforation erosion, the DAS signal weakens. There is a random dynamic change in the flow distribution between multiple clusters, which affects the uniformity of multi-cluster fluid injection. The number of effective clusters with fluid injection is correlated with operation pressure. Precautions such as temporary blocking, and pump stopping and restarting can intervene in the flow distribution between clusters, and the temporary blocking effect is influenced by multiple factors such as real-time state of fractures and temporary blocking parameters. There are two optic fiber DAS signal response modes for inter-segment leakage, which can reveal the leakage paths inside the casing and cement sheath. The optic fiber monitoring method and comprehensive analysis method have important reference values for an in-depth understanding of the mechanism of multi-stage multi-cluster fracturing of horizontal wells, guiding fracturing scheme optimization and real-time fracturing adjustment.